Pneumatic tire, and method for manufacturing same

ABSTRACT

The present invention prevents core deformation at a time of mounting a tire on a rim while corrosion resistance and air-leak resistance are assured in a tire made with a inner molding process. A bead core comprises axially inner and outer core pieces, and a radially inner end part of a carcass ply is held therebetween. The axially inner and outer bead pieces are composed of a spiral-wound body in which a bead wire has been spirally wound and overlapped. The bead wire comprises a core part in which core strands have been twisted together and a sheath part in which sheath strands have been twisted together around the core part. The core strands and/or the sheath strands comprise an embossed strand. The twisting direction and twisting pitch (Pc) of the core strands are the same as the twisting direction and twitching pitch (Ps) of the sheath strands.

TECHNICAL FIELD

The present invention relates to a pneumatic tire and a method formanufacturing the pneumatic tire having a bead structure comprisingaxially inner and outer core pieces, and a radially inner end part of acarcass ply is held therebetween.

BACKGROUND OF THE INVENTION

In recent years, to improve accuracy of tire forming, the followingmaking process (hereinafter called “inner molding process”) as shown inFIG. 8(A) is suggested:

-   -   using a rigid inner mold (a) comprising an outer surface shape        corresponding to a tire inner surface shape of a vulcanized        tire, and adhering tire structures member such as inner liner,        carcass ply, bead core, belt ply, sidewall rubber, tread rubber        and the like sequentially on this rigid inner mold (a) to form a        unvulcanized tire (t)    -   putting the unvulcanized tire (t) with the rigid inner mold (a)        into a vulcanizing mold (b), and    -   vulcanizing the tire between the rigid inner mold (a) and the        vulcanizing mold (b), which is an outer mold.

The inner molding process has difficulty terminating both end parts ofthe carcass ply around the bead core like in a traditional tire.

Therefore, the following Patent Document 1 shown in FIG. 8(B) disclosesa structure of dividing the bead core (d) into axially inner and outercore pieces (d1, d2) and compressing between the axially inner and outercore pieces d1, d2 without being turned-up the both end of the carcassply (c). Each of the core pieces d1, d2 is formed as a thin spiral-woundbody comprising a single bead wire (e) wound from a radially inner sideto a radially outer side in an overlapping manner in the shape ofspiral. This improves a radial height of the bead core (d) in thelimited winding number of the bead wire (e) to a maximum extent,increases an area of contact with the carcass ply, and ensures lockingon the both end parts of the carcass ply.

However, in case of such a bead structure, each of the core pieces d1,d2 is axially thin. Therefore, at the time of a rim mounting, therearises a localized deformation when twisting the bead portion with alever, and this becomes a plastic deformation; accordingly, thisdeformation will not return to its original shape after the rimmouthing.

CONVENTIONAL ART DOCUMENT Patent Document

-   Patent Document 1: Japanese unexamined Patent Application    Publication No. 2006-160236

GENERAL DESCRIPTION OF THE INVENTION Problems to be Solved by theInvention

Therefore, the present invention is based on employing the predeterminedtwisted structure of using plural of steel strands as substitute for asingle wire as the bead wire. And the present invention aims to providea pneumatic tire and a method for manufacturing the pneumatic tire whilekeeping corrosion resistance and air-leak resistance and providing inthe bead wire with an appropriate flexibility so as to prevent a coredeformation at the time of rim mounting.

Means for Solving the Problem

To solve the above-mentioned problems, the invention as set forth inclaim 1 is a pneumatic tire comprising a carcass comprising a carcassply extending from a tread portion through a sidewall portion to a beadcore of a bead portion. The bead core comprises axially inner and outercore pieces, and a radially inner end part of the carcass ply is heldbetween the axially inner and outer core pieces without being turned-uparound the bead core. Each of the inner and outer bead pieces arecomposed of a spiral-wound body in which a bead wire is wound from theradially-inwardly to the height of over the radially outer end of a rimflange in an overlapping manner in the shape of spiral. The bead wirecomprises a core part made of not less than two core strands twistedtogether and a sheath part made of not less than three sheath strandstwisted together around the core part, the diameter of the core strandsis the same as the diameter of the sheath strands, and the core strandsand/or sheath strands include an embossed strand that is embossed in awave shape before twisting. The twisting direction and the twistingpitch Pc of the core strands are the same as a twisting direction andtwisting pitch Ps of the sheath strands.

The invention as set forth in claim 3 is a method for manufacturing apneumatic tire comprising a carcass comprising a carcass ply extendingfrom a tread portion through a sidewall portion to a bead core of a beadportion. By use of rigid inner mold provided on an outer surface withthe tire forming surface forming a cavity surface of the pneumatic tire,the method comprises a green tire forming process to form a raw cover byadhering sequentially unvulcanized tire component members including thebead core and the carcass ply on the tire forming surface. The greentire forming process comprises: a first core pieces process to form anaxially inner core piece on the tire forming surface by spirally windingand adhering a rubber lining bead wire covered with unvulcanized rubberfrom the radially inward to radially outward in an overlapping manner inthe shape of spiral, a carcass forming process to have a step ofadhering the radially inner end part of the carcass ply on the axiallyoutside of the axially inner core piece, and a second core piecesprocess to form an axially outer core piece on the axially outside ofthe radially inner end part of the carcass ply by spirally winding andadhering the rubber lining bead wire from the radially inward toradially outward in an overlapping manner in the shape of spiral. Thebead wire comprises a core part made of not less than two core strandstwisted together and a sheath part made of not less than three sheathstrands twisted together around the core part. The core strands and/orsheath strands include an embossed strand that is embossed in a waveshape before twisting. The twisting direction and twisting pitch Pc ofthe core strand are the same as the twisting direction and twistingpitch Ps of the sheath strands.

Each of the inventions as set forth in claim 2 and 4; the bead wirecomprises the sheath strands wound around the core part after twistingthe core strands.

Effects of the Invention

As above stated, in the bead structure of the present invention, theradially inner end part of the carcass ply is held between the axiallyinner and outer core pieces. Each of the core pieces is made of aspiral-wound body which is made of a bead wire spirally wound andoverlapped to the height of over a radially outer end of a rim flange.Therefore, this improves the area of contact of core pieces with thecarcass ply and exerts the securing force sufficiently, and prevents ablowout of the carcass ply.

For the bead wire, a twisted structure is employed. The twistedstructure comprises a core part made by twisting the core strands and asheath part made by winding the sheath strands around the core part. Thetwisting direction and a twisting pitch Pc of the core strands are thesame as a twisting direction and a twisting pitch Ps of theabove-mentioned sheath strands. This provides the appropriateflexibility to the bead wire so as to prevent a core deformation at thetime of rim mounting.

Furthermore, the core strands and the sheath strands have the sametwisting direction and the twisting pitch one another. The strand can betwisted the most compatibly as well as a so-called bundle twistedstructure where plural of strands are tied together and twisted. Thishelps to form less spaces in the wire, to keep a deformation in the samedirection as a variation of the cross-sectional shape of the wire low,to improve the connecting power with the rim, and to keep the steeringstability. when an ordinal layer twisted structure that at least one ofthe twisting direction and twisting pitch are differs, there is a spacewhere the sheath strand may drop in the core part, the connecting powerwith the rim decreases, and this impacts negatively on steeringstability.

In the bundle twisted structure, locations of the strand on the wirechange at random, and the cross-sectional shape is unequal in thecircumferential direction. Therefore, in the circumferential direction,this structure is liable to have differing strengths of the connectingpressure with the rim. This weak connecting pressure area causes a dropof the air-leak resistance such that the fill up air is easier to leak.However, the above-mentioned twisted structure has a cross-sectionalshape stabile in the circumferential direction without changing thelocations of the strand, and this helps to keep the air-leak resistancehigh.

Moreover, the above-mentioned bead wire comprising an embossed strandcan improve rubber penetrating into the wire, can prevent corrosion, andcan improve the durability of the bead wire, furthermore the durabilityof the tire. Meanwhile, the bundle twisted structure with an embossedstrand improves the rubber penetrating to some extent, but the locationsof the strand changes randomly. The embossed strand forms interspacesunstably, thereby decreasing the rubber penetrating. However, in theabove-mentioned twisted structure, the locations of the strand do notchange, and the interspaces are formed stably. The twisted structure hasmore enhancing effects in rubber penetrating than the bundle twistedstructure.

The bundle twisted structure has a strong point of keeping the steeringstability while improving the connecting power with the rim and a weakpoint of having less air-leak resistance and rubber penetrating. Thebead wire having the twisted structure can exert the strong point andredeems the weak point of the bundle twisted structure. In the pneumatictire formed in the inner molding process, this suppresses the beaddeformation at the time of rim mounting without deteriorations of theblowout of the carcass ply, the connecting power with rim, the air-leakresistance and the rubber penetrating.

BRIEF EXPLANATION OF THE DRAWING

FIG. 1 is a cross-sectional view of a pneumatic tire showing anembodiment of the present invention.

FIG. 2 is a cross-sectional view of its bead portion enlargedly.

FIG. 3 is a cross-sectional view of inside structure of a bead wire.

FIG. 4 is a side view of an embossed strand.

FIG. 5 is a perspective view explaining a twisting method of the beadwire on a conceptual basis.

FIG. 6 is a cross-sectional view showing a green tire forming process.

FIGS. 7(A) to (C) are cross-sectional views showing a first core pieceprocess, a carcass forming process and a second core pieces process.

FIG. 8 (A) is a cross-sectional view explaining an inner moldingprocess, FIG. 8 (B) is a cross-sectional view showing a bead structureof a tire which the inner molding process is applied to.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will beparticularly described.

As shown in FIG. 1, a pneumatic tire 1 of the present embodimentcomprises a carcass 6 extending from a tread portion 2 through asidewall portion 3 to a bead core 5 of a bead portion 4. In the presentembodiment, a belt layer 7 is provided on a radially outside of thecarcass 6 and on an inside of the tread portion 2.

The belt layer 7 comprises at not less than one, two belt plies 7A, 7Bin the present embodiment, having belt cords inclined at an angle of 10to 35 degrees with respect to the tire circumferential direction. In thebelt layer 7, the belt cords intersect one another between the ply so asto improve the belt rigidity and reinforce strongly a substantiallyoverall width of the tread portion 2 with hoop effect. For the beltcord, a steel cord is employed in this embodiment, but high modulusorganic fiber cord such as polyethylene naphthalate (PEN), polyethyleneterephthalate (PET), aromatic polyamide and the like can be employed asappropriate.

A band layer 9 may be provided on the radial direction outside. The bandlayer 9 has organic fiber band cords such as nylon and the like woundspirally at an angle of not more than 5 degrees with respect to thecircumferential direction to improve the high-speed durability and thelike. For this band layer 9, a pair of edge band ply covering only theaxially outer end of the above-mentioned belt layer 7 and a full bandply covering the substantially-overall width of the belt layer 7 can bearbitrarily employed; and in the present embodiment, employed is asingle full band ply.

The carcass 6 comprises not less than one carcass ply 6A having organicfiber carcass cords arranged in radial arrangement, one carcass ply 6Ais applied in this embodiment. This carcass ply 6A forms a toroidalshape extending between the bead portions 4, 4. The both radially endparts 6AE of the carcass ply 6A terminates in the bead core 5 withoutbeing turned-up around the bead core 5. In concrete terms, the bead core5 is made of axially inner and outer core pieces 5 i, 5 o, and each ofthe radially end parts 6AE of the carcass ply 6A is held between theseaxially inner and outer core pieces 5 i, 5 o.

Each of the axially inner and outer core pieces 5 i, 5 o is, as shown inFIG. 2, composed of a thin spiral-wound body in which the bead wire 5 ais wound from the radially-inwardly to the height over a radially outerend of a rim flange RF in an overlapping manner in the shape of spiral.That is to say, radially heights H1, H2 measured from a bead base lineBL to the radially outer surface of the core pieces 5 i, 5 o are largerthan a radially height Hr measured from the bead base line BL to theouter end of the rim flange RF. In the core pieces 5 i, 5 o of thepresent embodiment, the bead wire 5 a is overlapped on one line in thetire axial direction. This improves the radially heights H1, H2 of thecore pieces 5 i, 5 o in the limited number of winding of the bead wire 5a to a maximum extent, and improves the area of contact with the carcassply 6A, and keeps the securing power of the both end parts 6AE of thecarcass ply 6A.

To prevent a core break at the time of tire deformation, this embodimentlimits the winding number No of the bead wire 5 a in the axially outercore piece 5 o to have less than the winding number Ni of the axiallyinner core piece 5 i. The bead portion 4 comprises the inner and outerbead apex rubber 8 i, 8 o extending from the axially inner and outercore pieces 5 i, 5 o toward respective radially outward tapered shape soas to reinforce a portion between the bead portion 4 and the sidewallportion 3. And, a symbol 10 in the drawings means a chafer rubber forpreventing rim shifting.

The bead wire 5 a is formed by twisting plural of steel strands 11having the same diameter to prevent the core deformation at the time ofrim mounting. In concrete terms, the bead wire 5 a comprises a core part12 made of not less than two core strands 11 c twisted together, and asheath part 13 made of not less than three sheath strands 11 s twistedtogether around the core part 12 as shown in FIG. 3. The twistingdirection and the twisting pitch Pc of the core strands 11 c are thesame as a twisting direction and twisting pitch PS of the sheath strands11 s. FIG. 3 shows an embodiment that the bead wire 5 a comprises twocore strands 11 c and seven sheath strands 11 s.

In this twisted structure of the present embodiment, since the twistingdirection and the twisting pitch Pc of the core strands 11 c are thesame as the twisting direction and the twisting pitch Ps of the sheathstrands 11 s, plural of strands 11 are arranged the most compactly andare twisted in the retaining of this arrangement. That is to say, thearrangement of the strands 11 in the wire section is the same onarbitrary longitudinal positions of the bead wire 5 a, and the samearrangement is maintained around the wire center.

In case of the bundle twisted structure, the strands locate mostcompactly, but the position of the strands in the wire changes randomlythereby varying the arrangement of the strands in the longitudinaldirection. Therefore, its cross sectional shape is non-uniform in thecircumferential direction and it is liable to lack in uniformity of theconnecting pressure with the rim in the circumferential direction. Itcauses a decrease of the air-leak resistance such as a fill up airleaking from the weak point of connecting pressure. However in thetwisted structure of the present embodiment, the strand positions do notchange, and the cross sectional shape is stable in the circumferentialdirection. Therefore, the air-leak resistance can be kept high.

In the case of the ordinarily layer twisted structure where at least oneof the twisting direction and twisting pitch differs, the core part andthe sheath part are distributed. Therefore, there is a space where thesheath strand drops into the core part, and a deformation in thedeforming direction of the cross sectional shape of the wire is liableto occur. This negatively affects on the steering stability such as adecrease of the connecting power with the rim. However, the twistedstructure of the present embodiment has a compact strand arrangement andforms the above-mentioned space as little as the bundle twistedstructure; therefore, it increases the connecting power with the rim andcan keep the steering stability.

The twisted structure of the present embodiment has the compact strandarrangement; therefore, the twisted structure has less rubberpenetrating into the wire. However, in the present embodiment, as shownin FIG. 4, the core strands 11 c and/or sheath strands 11 s includes anembossed strand 14 embossed in spirally or wavy shape before twisting.Thus, the embossed strand 14 helps to improve the rubber penetratinginto the wire, to reduce the development of rust, and to improve thebead wire durability and tire durability. Meanwhile, also in the case ofusing the embossed strand in the bundle twisted structure, the rubberpenetration can be improved to a certain degree, but the positions ofthe strands randomly change; therefore, the formation of the interspaceis precarious, and the rubber penetrating decreases. However, in thecase that the above-mentioned twisted structure, the positions of thestrands do not change; therefore, the interspace is stably-formed, andthe rubber penetrating is higher than that of the bundle twistedstructure.

In this way, the above-mentioned bead wire 5 a has the advantages of thebundle twisted structure of improving the connecting power with the rimso as to keep the steering stability, and can cover disadvantages of thebundle twisted structure such as less air-leak resistance and lessrubber penetrating. In the pneumatic tire made with an inner molding,the bead deformation at the time of rim mounting can be reduced withoutdeterioration of the blowout of carcass ply, connecting power with rim,air-leak resistance nor rubber penetrating.

A dimension K of embossing by the above-mentioned embossed strand 14(shown in FIG. 4) is preferably in a range of from 0.02 to 0.25 mm. Whenit is less than 0.02 mm, the rubber penetrating is not enough. When itis more than 0.25 mm, the dimension is unstable, and it has negativeeffects on the connecting power with the rim and the air-leakresistance.

A diameter of the strand 11 is not particularly limited, but from theaspect of the required strength of the bead wire, it is preferably in arange of from 0.175 to 0.45 mm for a passenger car tire. The number ofthe core strand 11 c and the number of the sheath strand 11 s are alsonot particularly limited, from the aspect of the required strength ofthe bead wire, the number of the core strand 11 c is preferably in arange of from 2 to 5 for a passenger car tire, the number of the sheathstrand 11 s is preferably larger than the number of the core strand 11 cand in a range of from 3 to 12.

As shown conceptually in FIG. 5, to achieve the above-mentioned compactstrand arrangement, it is preferably to form a core part 12 by twistingtogether the core strands 11 c, and after that the sheath strands 11 sare preferably wound around the core part 12. A symbol 20 in the drawingmeans a first twisting die provided around the center line with guideholes 20 a to give pass through each core strand 11 c. The firsttwisting die 20 is rotated around the center line so as to twisttogether the core strands 11 c for forming the core part 12. A symbol 21means a second twisting die provided around the center line with guideholes 21 a where each sheath strand 11 s pass through. The secondtwisting die 21 is provided in its center with an expansion insertionhole 21 b where the above-mentioned core part 12 is inserted. Thisrotation of the second twisting die 21 around center line forms thesheath part 13 by winding the sheath strands 11 s around the core part12. A symbol Qs means a converging position of the sheath strands 11 sand is located more forward than a converging position Qc of the corestrands 11 c. By adjustment of rotation numbers of the first twistingdie 20 and the second twisting die 21, the bead wires 5 a can be formedso as to have equal twisting pitches Pc, Ps. since the convergingposition Qc differs from the converging position Qs, a bead wire 5 a canbe obtained, where position changes are more surely prevented betweenthe core strand 11 c and the sheath strand 11 s.

The following is a method for manufacturing the above-mentionedpneumatic tire 1. As shown roughly in FIG. 6, this method formanufacturing uses a rigid inner mold 30 provided on an outer surfacewith the tire forming surface 30 s to form a cavity surface of thepneumatic tire 1 and comprises

a green tire forming process S1 to form a raw cover 1N by adheringsequentially unvulcanized tire component members on a tire formingsurface 30 s; and

a vulcanizing provide to vulcanize the raw cover 1N with the rigid innermold 30 in a vulcanizing mold (not shown)

As shown in FIGS. 7 (A) to (C), the green tire forming process S1comprises

(1) a first core pieces process S1 to form an axially inner core piece 5i on the tire forming surface by spirally winding and adhering a rubberlining bead wire 5 a covered with unvulcanized rubber from the radiallyinward to radially outward in an overlapping manner in the shape ofspiral,

(2) a carcass forming process S1 b to have a step S1 b 1 of adhering theradially inner end part 6AE of the carcass ply 6A on the axially outsideof the axially inner core piece 5 i, and

(3) a second core pieces process S1 c to form an axially outer corepiece 5 o on the axially outside of the radially inner end part 6AE ofthe carcass ply 6A by spirally winding and adhering the rubber liningbead wire 5 a from the radially inward to radially outward in anoverlapping manner in the shape of spiral.

The bead wire 5 a is formed with the above-mentioned twisted structure.As described above, the core strands 11 c has the same twistingdirection and twisting pitch Pc as the twisting direction and twistingpitch Ps of the sheath strands 11 s.

Although the especially preferred embodiments of the invention have beendescribed in detail, needless to say, the invention is not limited tothe above-mentioned concrete embodiments shown in drawings, and variousmodifications can be made.

EXAMPLES

To ascertain the efficacy of the present invention, a pneumatic tire(195/65R15) was made with an inner molding process by use of a bead wirehaving a structure shown in FIG. 1 and having a specification shown inTable 1. Each test tire was tested on deformation performance of a beadcore at a time of mounting on a rim, air-leak resistance of the beadcore, corrosion resistance of the bead wire, and steering stability; andthe results were compared. Traditional Example uses a single wire forthe bead wire. An embossed strand was employed for a sheath part. Thetwisting direction of the core strands and the twisting direction of thesheath strands were the same in both of Comparative Example and Example.

Twisted structures shown in Table 1 are as follows:

1×m structure: Bundle twisted structure with m numbers of the strand;

m+n structure: Layer twisted structure with th m numbers of the corestrand and n numbers of sheath strand; and

m/n structure: Twisted structure of the present embodiment with the mnumbers of the core strand and the n numbers of the sheath strands whichhave the same in twisting direction and twisting pitch.

Each test tire had substantially the same specification except for thespecification of the bead wire shown in Table 1. Primary commonspecifications were as follows:

<Carcass>

Number of carcass plies: 1

Material of carcass cord: polyester

Angle of carcass cord: 88 degrees (with respect to tire equator)

<Belt Layer>

Number of belt plies: 2

Material of belt cord: steel

Angle of belt cord: +28 degrees, −28 degrees (with respect to tireequator)

<Bead Core>

Winding number Ni of bead wires in axially inner core piece: 8

Winding number No of bead wires in axially outer core piece: 11

Rubber hardness of bead apex rubber: 80 (durometer A hardness)

<Cord Strength>

Based on the tension test of JIS (Japanese Industrial Standards) G3510of “Testing methods for steel tire cords”, maximum tension load of cordbreaking was measured. clamping distance was 700 mm, and tension ratewas 50 mm/min.

<Bending Rigidity>

By use of Taber V-5 Stiffness Tester, Type 150-D, manufactured by TABER(USA), a cord extending 5 cm from a fixed end is exerted pressure at itstip. Bending rigidity was defined as a value of bending moment (gf·cm)at the time that the tip aperture angle θ (theta) was at 15 degrees.

<Twisting Accumulation>

Visually evaluating a coming-off of the strand in a time of rubberlining to the cord.

(1) Deformation Blowout of Bead Core:

visually checking whether the bead core never recovered from adeformation at the portion the most twisted by a lever after dismountinga tire from a rim by use of a commercially available tire changer.

(2) Air-Leak Resistance of Bead Core:

The tire was mounted on a rim (15×6 JJ) and inflated to an internalpressure of 200 kPa, and remained untouched for 30 days. Evaluation wasdefined as a decreasing rate of the internal pressure using indices withthe traditional tire being 100. The larger the numeric value was, themore favorable the air-leak resistance was.

(3) Corrosion Resistance:

The tire was remained untouched for 21 days in a moist heat oven at atemperature of 70 degrees C. and 95% relative humidity and conducted anendurance test with a drum test run machine. The endurance test wasconducted under a condition of the tire internal pressure of 190 kPa,load of 6.96 kN, speed of 80 km/H, running for 375 hours in a row. Afterthe run, the tire was taken down and checked rust occurred in the beadwire. Evaluation was displayed on a scale of one to five. The larger thenumeric value was, the more favorable the corrosion resistance was.

(4) Steering Stability:

Each test tire was mounted on a rim (15×6 JJ) under an internal pressure(200 kPa) for all wheels of a vehicle (2000 cc). straight runningperformance, cornering stability, braking behavior and the like weretested by a professional driver when the vehicle ran on an asphaltedroad surface of a tire test course in dry condition. Evaluation wasperformed in the driver's feeling test and defined using indices with atraditional tire being 100. The larger the numeric values, the morefavorable the steering stability was.

TABLE 1 Traditional Comparative Comparative Comparative Comparative<Bead wire> Ex. Ex. 1 Ex. 2 Ex. 1 Ex. 3 Ex. 4 Ex. 2 Twisted structureSingle wire 1 × 9 2 + 7 2/7 1 × 11 3 + 8 3/8 Strand diameter <mm> 1.200.38 0.37 0.37 0.38 0.37 0.37 Numbers of core strands 1 — 2 2 — 3 3Numbers of sheath strands 0 — 7 7 — 8 8 Numbers of embossed strands — 44 4 4 4 4 Embossing type — Wavy Wavy Wavy Wavy Wavy Wavy Embossingdimension K <mm> — 0.17 0.17 0.17 0.17 0.17 0.17 Embossing pitch <mm> —4.71 4.71 4.71 4.71 4.71 4.71 Twisting pitch Pc of core <mm> — 26 10 2626 10 26 Twisting pitch Ps of sheath <mm> — 26 20 26 26 20 26 Cordstrength <N> 1206 3050 3050 3050 3725 3725 3725 Bending rigidity <gf ·cm> More than 500 256 231 231 282 282 282 Twisting accumulation —Generated None None Generated None None Deformation of bead coreGenerated None None None None None None Air-leak resistance of bead core100 90 100 100 90 100 100 Corrosion resistance of bead wire 4.5 2.5 4.54.5 2.0 4.5 4.5 Steering stability 100 100 80 100 100 80 100

From the result shown in Table, the cord of the embodiment was confirmedthat the bead deformation at the time of mounting on the rim could bereduced without reductions of the connecting power with the rim,air-leak resistance, nor rubber penetrating.

EXPLANATION OF THE REFERENCE

-   2 Tread portion-   3 sidewall portion-   4 Bead portion-   5 Bead core-   5 a Bead wire-   5 i Axially inner core piece-   5 o Axially outer core piece-   6 Carcass-   6A Carcass ply-   11 Strand-   11 c Core strand-   11 s Sheath strand-   12 Core part-   13 Sheath part-   14 Embossed strand-   S1 Green tire forming process-   S1 a First core piece process-   S1 b carcass forming process-   S1 c Second core piece process

1. A pneumatic tire comprising a carcass comprising a carcass plyextending from a tread portion through a sidewall portion to a bead coreof a bead portion, wherein said bead core comprises axially inner andouter core pieces, and a radially inner end part of the carcass ply isheld between the axially inner and outer core pieces without beingturned-up around the bead core; each of said inner and outer bead piecesare composed of a spiral-wound body in which a bead wire is wound fromthe radially-inwardly to the height of over the radially outer end of arim flange in an overlapping manner in the shape of spiral; said beadwire comprises a core part made of not less than two core strandstwisted together and a sheath part made of not less than three sheathstrands twisted together around said core part, the diameter of the corestrands is the same as the diameter of the sheath strands, and said corestrands and/or sheath strands include an embossed strand that isembossed in a wave shape before twisting; the twisting direction and thetwisting pitch Pc of said core strands are the same as a twistingdirection and twisting pitch Ps of the sheath strands.
 2. The pneumatictire as set forth in claim 1, wherein said bead wire comprises thesheath strands wound around the core part after twisting said corestrands.
 3. A method for manufacturing a pneumatic tire comprising acarcass comprising a carcass ply extending from a tread portion througha sidewall portion to a bead core of a bead portion, wherein by use ofrigid inner mold provided on an outer surface with the tire formingsurface forming a cavity surface of the pneumatic tire, the methodcomprises a green tire forming process to form a raw cover by adheringsequentially unvulcanized tire component members including the bead coreand the carcass ply on the tire forming surface; the green tire formingprocess comprises a first core pieces process to form an axially innercore piece on said tire forming surface by spirally winding and adheringa rubber lining bead wire covered with unvulcanized rubber from theradially inward to radially outward in an overlapping manner in theshape of spiral, a carcass forming process to have a step of adheringthe radially inner end part of the carcass ply on the axially outside ofsaid axially inner core piece, and a second core pieces process to forman axially outer core piece on the axially outside of the radially innerend part of said carcass ply by spirally winding and adhering saidrubber lining bead wire from the radially inward to radially outward inan overlapping manner in the shape of spiral; and said bead wirecomprises a core part made of not less than two core strands twistedtogether and a sheath part made of not less than three sheath strandstwisted together around said core part; said core strands and/or sheathstrands include an embossed strand that is embossed in a wave shapebefore twisting; and the twisting direction and twisting pitch Pc ofsaid core strand are the same as the twisting direction and twistingpitch Ps of the sheath strands.
 4. The method for manufacturing thepneumatic tire as set forth in claim 3, wherein said bead wire comprisesthe sheath strands wound around the core part after twisting said corestrands.